I would like to go on record saying that ISBN numbers are utterly
useless. Consider this:
* older books don't have ISBN numbers,
* the hardcover and softcover version of the same book have
completely unrelated ISBN numbers,
* different editions of a book have completely unrelated
ISBN numbers,
* even different printings of one and the same edition get
different ISBN numbers.
Because of this, it is impossible to reliably locate a book by ISBN in
a library or bookstore. The system is broken by design. A much more
rational way to code book references would be with the Library of
Congress classification codes (which can be found inside the front
cover of every book, right above the ISBN).
Axel